The general objectives of this project are to establish the pathways and study the enzymes involved in the biosynthesis of the diterpenoid gibberellin phytohorones and related diterpenoid substances with physiological activity. The relationship of these reactions to other aspects of isoprenoid reactions in the same tissues are being investigated along with factors which regulate and integrate all of these reactions. Current emphasis is on characterization of the electron transfer components and substrate specificities of the microsomal mixed function oxidases participating in the metabolism of kaurene and closely related intermediates of gibberellin biosynthesis in Echinocystis macrocarpa endosperm. A number of aspects of diterpene biosynthesis are being investigated in a cell-free extract of germinating castor bean (Ricinus communis) seedlings including (1) the purification and characterization of prenyl transferases and the synthetase for the formation of the diterpenoid phytoalexin casbene from both sterile seedlings and fungi-infected seedlings, (2) the purification of syntheses for the other diterpenes (ent-kaurene, ent- sandaraco pimaradiene, ent-beyerene and ent-trachylobane) produced in these extracts and the development of an affinity chromatography column useful in such purification studies, (3) the testing of cyclization substrate analogues, and (4) the nature of the fungal factors which induce casbene synthesis.